The present invention relates to packaging for products, such as food products, which are enclosed under certain environmental conditions in a support member having a lid which peelably delaminates (i.e., delaminates upon peeling) to expose a gas-permeable film, thereby causing a change in the environmental conditions within the package. More specifically, the invention relates to such packaging for fresh red meat products.
Historically, large sub-primal cuts of meat have been butchered and packaged in each supermarket. This arrangement has long been recognized to be inefficient and expensive. It would instead be preferable to butcher and package the meat at a central processing facility which benefits from economies of scale, and then ship the packaged meat to benefits from economies of scale, and then ship the packaged meat to individual supermarkets or other retail outlets such as is done, for example, with many poultry products. It is believed that central processing of meat would also lead to a higher quality, more sanitary product with a longer shelf-life than meat which is butchered and packaged in individual supermarkets.
Fresh red meat presents a particular challenge to the concept of centralized processing and packaging due to its oxygen-sensitivity. Such oxygen-sensitivity is manifested in the shelf-life and appearance (color) of a packaged meat product. For example, while a low-oxygen packaging environment generally increases the shelf-life of a packaged meat product (relative to meat products packaged in an environment having a higher oxygen content), red meat has a tendency to assume a purple color when packaged in the absence of oxygen or in an environment having a very low oxygen concentration, i.e., below about 5% oxygen. Unfortunately, such a purple color is undesirable to most consumers, and marketing efforts to teach the consumer about the acceptability of the purple color have been largely ineffective. When meat is exposed to a sufficiently high concentration of oxygen, e.g., as found in air, it assumes a bright red color which most consumers associate with freshness. After 1 to 3 days of such exposure, however, meat assumes a brown color which, like the purple color, is undesirable to most consumers (and indicates that the meat is beginning to spoil).
Thus, in order to effectively butcher and package meat products in a central facility for distribution to retail outlets, the meat would desirably be packaged, shipped, and stored in a low-oxygen environment for extended shelf-life, and then displayed for consumer sale in a relatively high-oxygen environment such that the meat is caused to "bloom" into a red color just before being placed in a retail display case. While in the retail display case, the meat product is desirably contained in a package which protects it from microbial and other contamination. In order to attain the maximum economic benefit from centralized packaging, the package in which the meat product is displayed for consumer sale is the same package in which the meat product is initially packaged and shipped from the central processing facility. As can be appreciated, centralized butchering and packaging of fresh red meat presents a number of difficult packaging challenges.
A variety of packages have been developed in an effort to overcome the foregoing challenges. One attempted solution is to use a dual-film cover or lid over a support member, such as an oxygen-barrier tray, which contains the meat product. The support member generally includes a cavity, in which the product is contained, surrounded by a peripheral flange to which the lid is secured. One film of the dual-film lid is relatively oxygen-impermeable, i.e., provides a substantial barrier to the passage of oxygen therethrough, and is removably positioned above a second film that is relatively oxygen-permeable, i.e., sufficiently permeable to the passage of oxygen to allow the packaged meat product to bloom. Thus, the package may be shipped with the upper, impermeable film intact so that a low-oxygen environment may be maintained within the package during shipping. Then the impermeable film may be removed at the supermarket just prior to placing the package in a retail display case. Since the lower film is oxygen permeable, it allows the meat product to bloom in the presence of oxygen which enters the package from the ambient atmosphere.
Conventional dual-film packaging arrangements can employ either separate, discrete permeable and impermeable lids which are attached separately to the support member, or a single, peelable lid which may delaminate into permeable and impermeable films. With the separate film approach, the permeable and impermeable lids are typically sealed to separate locations on the support member flange, with the permeable lid being sealed to an inner periphery of the flange and the impermeable lid being sealed to an outer periphery of the flange, i.e., outboard of the flange area at which the permeable lid is sealed. One drawback of this approach is the difficulty of sealing two separate lids to a conventional, single-flange tray in an automated fashion, i.e., continuously from separate permeable and impermeable webs of film. The permeable lid must be applied to the tray flange from a continuous web, secured (e.g., heat-welded) to an inner periphery of the flange, and then severed from the web in such a manner as to leave a sufficient area on an outer periphery of the flange to which the impermeable lid can be secured and severed from a continuous web of an impermeable film. Since this approach involves two separate lidding operations, it entails a relatively complex and expensive packaging procedure (as compared to a single-lid packaging operation). For example, it is difficult to sever the permeable lid from the web in such a manner that sufficient room is left on the outer periphery of the flange to provide a sealing surface for the impermeable lid without damaging the outer flange periphery. It is also difficult to completely remove atmospheric oxygen from the space between the permeable and impermeable lids.
While single, peelable lids have the advantage of providing a single web for sealing to a conventional tray flange, such films often fail during peeling, with the impermeable film either being difficult to delaminate from the permeable film or with all or part of the permeable film remaining bonded to the impermeable film and tearing away from the rest of the package, thereby resulting in tears or holes in the package which expose the packaged meat product to dirt or contamination. The primary difficulty in achieving consistent and reliable peelability in a single, peelable lid lies in the manner in which the permeable and impermeable films are adhered to one another. That is, with conventional peelable lids, the same mechanism which bonds the permeable and impermeable films is also relied upon to allow the two films to be peelably separated. Such mechanisms include, e.g., the use of heat and pressure (e.g., heated rollers) to bond the two films, or an adhesive layer sandwiched between and bonding the two films. The bond which is formed must be strong enough to prevent film separation during shipping and storage so that oxygen does not prematurely enter the package via the gas-permeable film (i.e., prior to the time when the retail worker intentionally peels the impermeable film from the permeable film). At the same time, the bond between the two films must provide sufficient peelability that the two films can be separated without tearing or otherwise compromising the permeable film as noted above. As can be readily appreciated, these are difficult and somewhat conflicting requirements to meet. Not only can the strength of the bond between the permeable and impermeable films vary due to manufacturing fluctuations, but the bond-strength can also change over time due to, e.g., migration of components (e.g., antifog agents) within one or both films to the interface between the films, temperature variations, etc., all of which can cause physical and/or chemical changes to the bond. In addition, it is often desirable that the the permeable film contain very small perforations (e.g., less than about 250 microns in diameter) in order to increase the rate at which the packaged meat product blooms after removal of the impermeable film. Conventional mechanisms for bonding the permeable and impermeable films often interfere with the ability of such perforations to allow atmospheric oxygen to pass therethrough after the impermeable film has been removed. For example, the use of heat and pressure to bond the two films can weld closed the perforations while an adhesive can occlude the perforations (i.e., partially fills the perforations and thereby blocks the passage of oxygen therethrough).
Accordingly, there is a need in the art for a duai-film package which combines the manufacturing simplicity of a package having a single, peelable lid with the consistent peelability of a package having separate permeable and impermeable lids.